[T10] Questions about SAS TX RX common mode return loss

Jiagongxian jiagongxian at huawei.com
Sun Nov 22 17:28:33 PST 2015

HI All,

I have a question related  to  SAS TX  RX  common mode return loss.

According to the SAS 3r06,   for 12Gbps TX, the common mode loss requirement is based on  Table 47,  -12 Gbit/s maximum limits for S-parameters at Its OR CTS, the common mode return loss SCC22 start at -6 dB at low freq. band,  which is measured  according to  method  based on Figure F. 19, using de=embedding to reach the connector footprint according to the  the document ( Section F.11.4.4,  Tx Rx connection S11 measurements at IT or CT).

Which means,  after de-embedding,  TX or RX return loss is mainly influenced by the connector, if the return loss of  SAS  connector is high than -6 dB at lower freq. band,  it will make the return loss of the device can not meet the spec. of TX or RX side of SAS device. Unfortunately, the  SAS connector requirement is defined in Table 7,which is start at -3 dB at low freq. band..

Compare Table 47 (return loss requirement of  SAS device) and Table 7 (return loss of  SAS connector ) ,  the common mode return loss of connector is about -3 dB at low freq. band, while  the common mode return loss of  SAS  device is  -6 dB at low freq. band, which make it is very hard for  the  device’s common mode return loss  to pass -6 dB spec.  at  some low  frequency band.

Is there anything wrong  with my analysis ?

Best regards

Jia Gongxian/贾功贤
Phone: 0755-89651131
Email: jgxian at huawei.com<mailto:jgxian at huawei.com>
Huawei Technologies Co., Ltd./华为技术有限公司
Bantian, Longgang District,Shenzhen 518129, P.R.China/深圳市龙岗区坂田华为基地,518129
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